"In its current form," said Geithner of the amendment, "it threatens to undermine the effective, carefully phased and sustainable approach," the administration is currently advocating.

The amendment would specifically disallow organizations that do business with financial institutions in Iran, including the countries central bank, from holding financial accounts in the United States. Waivers though would be provided for companies that deal with national security matters.

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The amendment also requires that studies be done to better understand how oil prices would be affected in the United States.

"There is absolutely a risk that in fact the price of oil would go up, which would mean that Iran would in fact have more money to fuel its nuclear ambitions, not less," said Wendy Sherman, the State Department's undersecretary for political affairs.

EU foreign ministers meeting in Brussels on Thursday also applied more pressure on Iran. According to Maja Kocijancic, a spokeswoman for EU foreign policy chief Catherine Ashton, the ministers agreed on new sanctions that apply to 143 entities and 37 individuals.

Earlier in the week, Fars News, a semi-official Iranian news agency, reported that Seyed Emad Hossein, head of the Iranian Parliament's Energy Commission, warned the United States of continuing to sanction the country.

"Sanctions on Iran's oil, gas and petrochemical industries would be synonymous with a disruption in the world market, which in turn would push up crude prices," Hossein warned.

"It is a very, very powerful threat," said David Cohen, Under Secretary of the Treasury at a congressional hearing. "It is a threat to essentially the commercial banks to end there ability to transact in the dollar and there ability really to function as major international financial institutions."

Democratic Sen. Robert Menendez of New Jersey and Republican Sen. Mark Kirk of Illinois sponsored the amendment, which now needs House approval and the president's signature to become law.

"The Central Bank of Iran is the primary bankroller of Iran's global terror network, its nuclear program and other illicit activities," said Kirk. "The time has come to impose crippling sanctions on this terrorist and nuclear-financing institution."

Passage of the bill was part of a larger defense authorization bill that includes a new policy for detaining and trying suspected al Qaeda terrorists -- a policy that attracted controversy during the debate and may draw a presidential veto.